The present invention relates generally to motor control systems, and more particularly, to a motor control center subunit having a clutch system which governs the limits of extension and retraction of power circuitry within the motor control center subunit. In one embodiment, the system and method described herein allow translation of power circuitry along a threaded drive after full installation of the motor control center subunit into the motor control center. Translation of the power circuitry occurs between a position wherein the power circuitry is engaged with a power bus and a position wherein the power circuitry is retracted from the power bus. Once power circuitry reaches either the engaged or retracted position, the clutch system causes the drive to spin freely and thus prevents movement past either the engaged or retracted position.
A motor control center is a multi-compartment steel enclosure with a bus system to distribute electrical power, on a common bus system, to a plurality of individual motor control units mountable within the compartments. The individual motor control center subunits are commonly referred to as “buckets” and are typically constructed to be removable, pull-out units that have, or are installed behind, individual sealed doors on the motor control center enclosure. These buckets may contain various motor control and motor protection components such as motor controllers, starters, contactor assemblies, overload relays, circuit breakers, motor circuit protectors, various disconnects, and similar devices for electric motors. The buckets connect to the supply power lines of the motor control center and conduct supply power to the line side of the motor control devices, for operation of motors. Motor control centers are most often used in factories and industrial facilities which utilize high power electrical motors, pumps, and other loads.
Typically, when installing or removing motor control center buckets, the power supply lines are connected. To remove such a bucket, a deadfront door of the bucket or of the motor control center is opened and an operator manually pulls on the bucket to separate the primary disconnects, or “stabs,” from the bus system, thereby disconnecting the power supply. Installation of a bucket is accomplished in a similar manner, wherein the operator manually pushes the bucket into a compartment of the motor control center to engage the bucket stabs with the bus system, thus connecting the system to supply power. The line connections or stabs may be difficult to maneuver manually when an operator is supporting the entire bucket or when the stabs are not visible.
Attempts have been made to improve upon the manual installation and disconnection of motor control center buckets and supply power connections from live supply power lines, risers, and/or a vertical bus of a motor control center. Other systems have employed pivotable handles inside the buckets to pivot line connectors to and from supply lines. However, many of these systems require that the bucket or compartment door be open to manipulate the handles and line stabs. Additionally, these systems can subject the pivot line connectors and other components to overdrive and/or overtorquing, as the system includes solid stops when manipulating the connectors between racking in and extracting out positions.
It would therefore be desirable to design a motor control center bucket assembly that overcomes the aforementioned drawbacks. Thus, it would be desirable to provide for remote connection or disconnection of the line stabs of a bucket to the power supply lines or bus of a motor control center from a distance. In the event of an arc or arc flash, any heated gas, flame, and/or the arc itself should preferably be contained behind the bucket compartment door or “deadfront.” Furthermore, as connection or disconnection of the line stabs is to be completed remotely, it would be desirable to provide a means to prevent overdrive or overtorquing during remote connection or disconnection of the line stabs.